There has been known a wireless power transfer system that wirelessly transmits electric power. The wireless power transfer system is provided with a power transmitter including a power transmission coil, and a power receiver including a power reception coil, and the system achieves wireless power transmission using electromagnetic induction, magnetic resonance, or the like between the coils. The wireless power transfer system is applicable to, for example, a charging system of an electric vehicle. In this case, the electric power that is wirelessly transmitted is supplied to a battery.
To the battery, it is necessary to supply a direct current (DC) signal. In signal conversion and signal processing in the wireless power transfer system, however, a ripple (fluctuation) may be caused to the DC signal. It is desired that such ripple be removed. In Patent Literature 1, for example, there is described a technique for reducing the ripple caused to the electric power received by the power reception coil by controlling a voltage of the power transmission coil. In the technique described in Patent Literature 1, in order to suppress strength of an electromagnetic field generated around the power transmission and reception coils, the ripple, which is caused by spreading a frequency of the electric power supplied to the power transmission coil, is to be removed.
As described in Patent Literature 2, as a control of the electric power transmitted in the wireless power transfer system, there has also been known a combination of a first feedback control (feedback control based on a first characteristic value) and a command value correction control (correction feedback control based on a second characteristic value).